Multi-layered polymer materials consisting of different polymers, or laminated films and sheets, are able to achieve combined properties that cannot be obtained from a single material while minimizing unwanted characteristics. Thus, this structure has been widely used for packaging application, by combining cheap and mechanically strong polymers (e.g. polypropylene (PP) or polyethylene (PE) with moisture or oxygen barrier polymer (e.g. EVOH).
Besides, in US patent application publication No. 20100172066A1, there is disclosed a multilayer polymer dielectric film comprising a first dielectric layer and a second dielectric layer which are coextruded. The first dielectric layer and the second dielectric layer comprise different polymer materials, one with high dielectric permittivity and the other with high dielectric strength. Under optimal condition, the coextruded laminate films composed of alternating layers with the two different polymer materials are able to provide dielectric strength higher than either of individual materials with combined dielectric permittivity. However, the manufacturing process for such a multilayer polymer dielectric film is limited by the compatibility of thermal and rheological properties between different polymers, which is challenging and particularly important for co-extrusion process. For instance, due to its low melting flow index, the electric insulation grade of PP is difficult to be coextruded with other widely used co-extruded materials such as polyamide and PET with relatively high melting flow index.